Halogens are known to react readily with nitroalkanes. This reaction occurs with respect to the hydrogens bonded to the same carbon as the nitro group. In the presence of an alkaline catalyst, complete halogenation of the nitroalkane is easily achieved. Thus, nitromethane reacts readily to produce chloropicrin in high yield as illustrated below. ##STR1##
Due to the ease with which complete halogenation takes place, however, it is difficult to prepare monohalogenated nitroalkanes in high yield. This difficulty is compounded by the difficulty in separating the monohalogenated product from any polyhalogenated product formed in the halogenation reaction.
A method of preparing monochlorinated nitromethane is described in U.S. Pat. No. 2,309,806. In this process, approximately equivalent quantities of aqueous solutions of nitromethane and a basic alkali metal hydroxide are reacted to form an alkali metal salt of the nitromethane which is, in turn, reacted with gaseous chlorine at a temperature not substantially in excess of 50.degree. C. to produce monochlorinated nitromethane. The monochlorinated nitromethane is subsequently recovered by distillation.
More recent U.S. Pat. No. 3,096,378 describes a method of preparing monochlorinated nitroethane. The described process consists of a rather rigidly controlled chlorination of nitroethane with a special emphasis being placed on the control of reaction vairiables such as agitation, temperature, and time of reaction. An aqueous solution of the sodium salt of nitroethane is prepared by adding a solution of sodium hydroxide to a slurry of nitroethane in water with cooling. Sodium chloride is added to the solution to decrease the solubility of the monochlorinated nitroethane to be formed in the aqueous solution. The solution of the sodium salt of nitroethane is then cooled to 0.degree. C. Chlorine is bubbled through the solution while avoiding stirring, and the monochlorinated nitroethane is formed and removed from the reaction mixture.